Accidental or purposeful exposure of people to high levels of radiation poses a serious immediate risk and potential long-term health risk. NO FDA approved radiomitigant effective 24-48h after radiation injury is available today. Thus, there is a critical unmet medical need to shield the population from these harmful effects of unintended radiation. We established that octadecenyl thiophosphate (OTP) administered 26 h after lethal levels of ?-irradiation by a single subcutaneous injection increases crypt counts and survival with a dose modification factor of 1.2. The overall objective of this application is to develop OTP as a gastrointestinal radiomitigator for use in human subjects exposed to lethal ionizing radiation either as a result of nuclear accident or terrorist attack. The deliverable will be non-human primate safety and efficacy data for a "drug master file" enabling the filing of an Investigational New Drug application based on the Animal Rule of the FDA. This work will be completed in collaboration between the Departments of Physiology, Pharmaceutical Sciences, and Pathology of the University of Tennessee Health Science Center, RxBio. Inc. and the California National Primate Research Center. The project is ready to be deployed upon funding and builds on previous collaboration of the research team. The Grand Opportunities program aims the "development of innovations" linked to public health. Development of OTP for the treatment of the gastrointestinal acute radiation syndrome - the primary objective of the present application - appears to hold significant promise for the benefit of mankind - and as such, stands to significantly impact the country and the world. Public Health Relevance Statement: NO FDA approved radiomitigant effective 24-48h after radiation injury is available today. This project will provide non-human primate safety and efficacy data for a "drug master file" for octadecenyl thiophosphate as a gastrointestinal radiomitigator for use in human subjects exposed to lethal ionizing radiation enabling the filing of an IND application based on the Animal Rule of the FDA.